Self-clamping grip for a free cable winch

ABSTRACT

A self-clamping grip for a free cable winch having two jaws capped on each end with respective straps. A drive for one of the straps actuates the other strap. Eccentrics housed in the straps raise the inner jaw which is free to move within a U-shaped outer jaw. A spring ensures the self-clamping action.

O United States Patent [191 [111 3,886,63 r

Caradot 1 June 3, 1975 SELF-CLAMPING GRIP FOR A FREE [56] References Cited CABLE WINCH UNITED STATES PATENTS [75] Inventor: Patrice Caradot, Saint-Etienne, 1,143,713 6/1915 Kirstin 254/76 France 1,449,945 3/1923 Jacobsen 24/134 L 3,142,879 8/1964 Faure.... 24/134 N Asslgneei Mllbras, France 3,410,525 11/1968 Tanson 24/134 NX Filed Dec 14 1972 3,528,139 9/1970 Desplats 254/76 X [21] Appl. No.: 315,110 Primary ExaminerRoy D. Frazier Assistant Examiner-William E. Lyddane [30] Foreign Applicamm Priority Data Attorney, Agent, or FtrmIrv1ng M. Werner DEC. 15, 1971 France 71.46247 [52] U S Cl 24/134 24/134 254/76 A self-clamping grip for a free cable winch having two jaws capped on each end with respective straps. A [51 1 Int Cl F16g 11/00 B66f 3/00 drive for one of the straps actuates the other strap. Ec- [58] Fie'ld WL 134 134 EA centrics housed in the straps raise the inner jaw which 24/134 KD, 134L, 134 N, 249 WL; 254/76,

i 21 91m e2 1 "l? is free to move within a U-shaped outer jaw. A spring ensures the self-clamping action.

10 Claims, 6 Drawing Figures Pmmmm ms 3886631 SHEET 1 EIG. 2

PAm-mmm 1975 3.886 631 SHEET 2 qfca. 3

SELF-CLAMPING GRIP FOR A FREE CABLE WINCH The present invention relates to improvements in self-clamping grips of the kind used in a so-called free cable" winch.

BACKGROUND OF THE INVENTION As is known, there are two main types of cable winches. The first one is the drum winch wherein driving means rotatingly drive the drum onto which the cable winds itself.

In contradistinction, a free cable winch is provided with two grips which pull in turn the cable to hoist same, so that the cable moves ahead through the winch, beyond which the end of said cable remains free.

The principle of such a free cable winch is disclosed, for instance, in French Pat. No. 687,232.

Substantial improvements have been brought to the design of the grips, for instance, by French Pat. No. l,45l,230, which teaches forming each grip from an outer U-shaped jaw disposed around an inner jaw, the clamping between the two jaws being obtained by cams which bear directly on the outer U-shaped jaw in order to press the inner jaw. This allows clamping the cable between the two jaws when the latter have to support the load.

In all the known embodiments, the cams have a double function, that is:

1. they bring about between the two jaws a clamping action sufficient to draw the cable;

2. after the clamping is effected, they bear the whole stress of the drawing of the cable by the grip concerned.

As the friction coefficient of a cable clamped by the jaws is about 20%, the cam pressing force required for clamping the jaws onto the cable in order to pull the latter is at least 6 times the pulling force proper for drawing the cable. This proportionality automatism between the clamping force of the jaws and the pulling force, according to a ratio of about 6:1, is obtained in a simple way in the known winches, by using two separate pairs of levers having no interconnection, except that each pair is keyed, on the one hand to the ends of the cam profiles, and, on the other hand, to the linking and driving axes for the mechanism. It is found that said lateral levers are necessarily thin, and transmit enormous clamping efforts through bearings having comparatively small surfaces. Thus. the two pairs of levers constitute deformable parallelograms, which tend to warp under the stresses, which brings about parasitic frictions between the various members of the winch. This results in deformations of parts and undue wear. Finally, these known systems can only be used for comparatively low power winches.

On the other hand, the known systems cannot be fitted to high power winches adapted, for instance, to exert a force of tons or more on a cable.

The object of the present invention is to avoid such drawbacks by providing a self-clamping grip arrangement adapted to be used on a high power free cable winch.

SUMMARY OF THE INVENTION The present invention provides a gripping apparatus fora free cable winch including a first aw member, and a second jaw member disposed adjacent the first aw LII member to form with the first jaw member a passage way through which a cable may selectively be pulled and clamped. The apparatus also includes eccentric push means bearing against the first jaw member. First strap means is disposed adjacent one end of the first and second jaw members, and second strap means is disposed adjacent the other end of the first and second jaw members. The gripping apparatus also includes link means. First pivot means is disposed on one side of the cable pivotally interconnecting the first and second strap means, the second jaw member, and the eccentric push means bearing against the first jaw member. Second pivot means is disposed on the other side of the cable pivotally interconnecting the link means and the first and second strap means. The gripping apparatus also includes resilient means connected between the second jaw member and the first strap means urging the jaw members to clamp together against the cable under the action of the eccentric push means.

A grip for a free cable winch according to the inven tion includes an inner jaw adapted to move within a U- shaped outerjaw by which said innerjaw is surrounded, these two jaws defining together a passageway receiving a cable, and is characterized in that the pair ofjaws is capped at one end by a first strap and at the other end by a second strap, each of said straps having a transverse back, the inner surface of which is provided with a pushpiece in the shape of an arc of a circle, which piece bears on the back of the inner jaw, while each strap pivots about a transverse axis which is likewise located behind the back of the inner jaw at a location which is set over with respect to the pushpiece, the free ends of the arms of one of the straps beyond the outer jaw being connected, on the one hand, to a stop on the outer jaw by a spring tending to rock the strap in the direction in which the jaws are clamped under the action of the set over pushpieces, and, on the other hand, to the free ends of the arms of the other strap by at least one pivoted link.

In the same way as in a free cable winch of known type, at least one of the two straps is provided with means ensuring the positive driving thereof through swinging round the axis thereof.

According to a further feature of the invention, each set over pushpiece is connected to the back of the inner jaw through a bi-directional connection, This connection is constituted, for instance, by pivoting the set over pushpiece in a housing in the back of said jaw, which housing surrounds said piece over more than Such a connection is obtained in the practice by securing a small block to the back of the inner jaw, after mounting each set over pushpiece in a cylindrical housing defining an angle lower than or equal to 180 in the back of said jaw, said block having one curved bearing surface which closes on the pushpiece and completes the cylindrical housing. According to a preferred embodiment, the back of the inner jaw is provided with a transverse dovetailed slot between the two semicylindrical housings, in which slot two tenons on the bases of the two small blocks come to fit transversely and in back-to-back relation. Owing to this arrangement, it is possible to fix the two small blocks merely by means of a screw which passes through the opposite half-notches thereof and engages in a hole tapped in the jaw. since the main operation stresses are received by the tenon and slot assembly.

According to an additional feature of the invention. each set over pushpiece is provided at its top with a plane bearing surface from which a boss projects. which boss is housed in a corresponding opening in the back of the strap before the welding of the assembly. so as to obtain a highly rigid structure.

An additional feature of the invention consists in providing on the back of the positively driven strap a small arm having a hole to receive the pivot pin ofa connecting rod or a control lever.

A further feature consists in providing in each solid set over pushpiece an inner cavity which opens on the cylindrical pushing wall so as to constitute a sealed grease tank, which is filled only once at the time of the assembly.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 illustrates a free cable winch equipped according to the invention.

FIG. 2 is a longitudinal section thereof.

FIG. 3 is an exploded view showing the whole of the component parts of a pair of clamping jaws in a free cable winch according to the invention.

FIG. 4 is a side view showing the upperjaw fitted with its set over pushpieces or eccentrics, the latter being shown before the fitting thereof onto the backs of the straps.

FIG. 5 is a side view, partly in section, showing the jaws in their positions of operation or rest. with selfclamping.

FIG. 6 is a similar view showing the jaws in their loosened position.

DETAILED DESCRIPTION OF THE INVENTION A free cable winch according to the invention is illustrated in FIGS. 1 and 2. This winch includes:

an outer casing 1;

a towing control lever 2, adapted to swing alternatively in the directions of arrows 3 and 4;

a release lever 5;

a handle 6 for handling the winch;

a fixing hook 7.

It is known that a winch of the above type is used by securing the hook 7 to a fixed point, and then swinging the lever 2 in the directions of the arrows 3 and 4. A cable 9, which tows a load not shown, is thus made to move forward in the direction of the arrow 8. This cable 9 passes through the winch over the whole length of the casing 1. Forward of the winch, the end 10 of the cable 9 remains free.

The motion of the cable 9 is obtained by means of two pairs ofjaws l1 and 12, received inside the casing I. Said jaws are connected with the end 13 of the lever 2 through a connecting-rod arrangement (not shown) known per se, the lever 2 swinging about a pin 14. Thus the pairs of jaws 11 and 12 are alternatively imparted a motion which brings them near each other (arrows l5 and 16) or away from each other. During said motions. one of the pairs ofjaws, for example, 12, is clamped on the cable 9, while the other. for example. 11, is open. and vice versa.

This principle of operation for a free cable winch is known per se. The present invention relates to a particularly advantageous embodiment of the pairs ofjaws 11 and 12. Since these two pairs ofjaws are of similar construction, only one of them will now be described in more detail. such as, for instance. the pair 11.

Said pair includes a first jaw member or upperjaw l7 and a second jaw member or lower jaw 18. The jaw 18 has a U-shaped transverse section. and embraces the jaw 17. while it rises on either side of the latter. The jaw 18 is provided at the tops of its lateral surfaces with two pairs of holes 19 and 20 intended for receiving first pivot means. such as pivot pins 21 and 22.

The assembly constituted by the two jaws l7 and 18 is embraced by first and second strap means. such as two straps 23 and 24, which, according to the invention, may be identical, that is. produced from the same machinery. The two limbs of the strap 23 extend on either side of the outer jaw 18, below which their ends are provided with holes 25 which lie opposite each other to receive a transverse pin 26 forming part of second pivot means. The strap 23 includes two stop shoulders 27 located below the holes 25, and a small plate 28 provided with a central finger 29 bears against said shoulders. The finger 29 is adapted to receive resilient means, such as the bearing coil 30 of a compression spring 31, which centers itself thereon. Said coil 30 ends in a hook 32 which. after assembling. fits round the pin 26 (FIGS. 3, 5 and 6).

The spring 31 has its opposite end provided with a bearing coil 33 which centers itself on a finger 34 integral with a shaft 35 which forms part of the jaw 18.

The strap 23 is provided near its top with two holes 36 disposed in opposite relation and adapted to receive the transverse pin 21. The latter is located above the back of the upper jaw 17.

The top of the strap 23 is provided with a transverse bottom 37, in which an opening 38 is preferably provided, which is, for instance. square or rectangular. This opening is intended for receiving the centering projection 39 which has the same profile. and is provided on the back of eccentric push means. such as a pushpiece or eccentric 40. Said eccentric is a solid member corresponding to an arc of a circle of about 270, set over with respect to a hole 41 which receives the pin 21. The rear portion of the eccentric is formed with a stop heel 43.

During the manufacture, the projection 39 is housed in the opening 38 in the bottom of the strap 23, and the assembly is finally welded (FIG. 6). The assembly thus obtained is particularly rigid, and adapted to transmit great forces at the level of the periphery of the eccentric 40 when the strap 23 swings about its pin 21.

A hollow 46 with a substantially semi-cylindrical profile is provided on the back of the upper jaw 17, said hollow being adapted to receive the eccentric 40. A transverse slot 47 with a dovetail profile is provided in front of the hollow 46, and is adapted to receive the dovetail tenons 42 and 44 of removable small blocks 45 and 49. These small blocks are fixed by means of a screw which passes therethrough over the whole height thereof at the level of half-notches and 61 with which the backs of said blocks are provided. The screw 50 engages in a hole 51 tapped in the bottom of the slot 47.

The small block 45 is provided rearwardly with a concave bearing surface 52, which forms a portion of a cylindrical surface having the same radius as the hollow 46.

After assembling (FIGS. 5 and 6). the hollow 46 and the concave surface 52 together define a cylindrical surface portion extending over about 270. Said concave cylindrical portion constitutes the female part of a housing inside which the eccentric 40 is received. The female portion 46 and 52 surrounds the eccentric 40 over an angle greater than 180, so that said eccentric remains trapped and cannot clear itself from the jaw 17. The latter is also subjected to a truly desmodromic drive, as will be seen further below.

The upper part of the rear portion of the jaw 17 defines an oblique bearing surface 53, which is adapted to receive the stop heel 43 so as to limit the swinging amplitude of the strap 23 when the latter is in a position where the jaws are loosened (FIG. 6).

The front strap 24 is designed in the same way as the strap 23, except that its top is provided with a welded arm 54 provided with a hole 55. Said hole is used for mounting the linkage ensuring the connection with the end 13 of the control lever 2.

Apart from this difference, the strap 24 is, like the strap 23, provided with:

two transverse holes 125 to receive a pin 126 forming part of the second pivot means;

an upper bottom 137 below which an eccentric 140 is welded;

two transverse holes 136 to receive the pin 22, the

latter passing also through a hole in the eccentric 140 forming part of the eccentric push means.

The eccentric 140 is likewise fitted into a hollow 146 in the back of the jaw 17. Said hollow 146 is completed by the concave bearing surface 152 of the retaining small block 49, the latter being assembled with the jaw 17 by means of its dovetail tenon 44.

Lastly, the pins 26 and 126 at the free ends of the straps 23 and 24 are interconnected by two pivoted lateral links 56.

Upon the mounting, the cable 9 is engaged between the bottom of the U-shaped jaw 18 and the base of the upper jaw 17.

Lastly, the ends of the pins 21 and 22 carry runners, which move within guiding slides 57 (FIG. 1) provided in a known way in the sides of the casing 1.

The operation is as follows:

When the operator actuates the lever 2, and transmits to the pin in the hole 55 an effort directed according to the arrow 58 (FIG. 5), the strap 24 tends to swing in the same direction abouts its axis pin 22. The connection through links 56 causes the strap 23 to swing in the same direction abouts its axis pin 21. Consequently, the two eccentrics 40 and 140 bear upon the back of the upperjaw 17 (arrow 59), which causes the cable 9 to be strongly clamped on the bottom of the U- shaped jaw 18. It will be noted that said clamping takes place by the two jaws 17 and 18 bearing directly upon each other. owing to the fact that each pin 21 or 22 takes its bearing directly in the bores 19 or in the jaw 18, while acting as an axis of rotation for the push eccentric or 140. None of the intermediate parts, such as links or the like, takes part in the transmission of the total effort developed between the two jaws 17 and 18 after reduction. As a result, the assembly has very great rigidity, which allows exerting much stronger pulls on the cable 9 than with the free cable winches of known types.

On the other hand, when the operation of the swinging lever 2 subjects the pin in the hole to the effort directed according to the arrow (FIG. 6). the strap 24 tends to swing in the same direction about its axis pin 22. The connection links 56 cause the strap 23 to swing in the same direction about its axis pin 21. Thus,

each eccentric 40 or rises as indicated by the arrow 61. Owing to the bi-directional connection between each eccentric 40 or 140 and the upperjaw 17, the latter is likewise raised in the direction of the arrow 61, 5 while remaining parallel to the bottom of the jaw 18. The cable 9 is thus freed, which enables the pair ofjaws 11 to move lengthwise with respect to said cable, while the other pair of jaws 12 remains clamped.

The function of the spring 31 is to cause automatically the straps 23 and 24 to rock in the direction of the arrow 58 (FIG. 5), that is, in the direction where the jaws 17 and 18 are clamped, when the winch is at rest, or during an intermediate stage of inversion of the direction of motion. The springs 31 have thus a starting action which ensures a safe utilization of the winch.

The main advantages of the arrangement according to the invention are as follows:

1. The machining of the eccentrics 40 and 140, the straps 23 and 24, and the jaws 17 and 18 includes only drilling operations or cut of cylindrical surfaces; in particular, no machining according to a more complete profile is required.

2. The assembly is particularly rigid, which allows exerting substantial clamping efforts on the cable 9, and increasing therefore the towing power of the winch.

3. As no intermediate members are required for transmitting the overall effort between the jaws 17 and 18, it is possible to make the pairs of jaws as assemblies taking up very little space: it becomes possible, in particular, to increase the length of the jaws 17 and 18 substantially, that is. to increase their areas of contact with the cable 9; this, in fact, makes it possible to increase the overall clamping effort on the cable, while locally reducing the specific pressures exerted on the periphery of said cable by the jaws l7 and 18; the wear of the cable is thus reduced, as compared with that in a conventional winch, in spite of the increase of the useful pull.

4. Mounting the springs 31, which start the selfclamping of the jaws, is particularly simple inasmuch as no coupling or connection with the casing 1 of the winch is required anymore.

5. The pivot pins 21 and 22 do not bear any torsional stress; the comparatively high stresses to which they are subjected in all cases are thus only shearing stresses, which the assembly according to the invention makes it possible to distribute in four planes (corresponding to the four bearing ends of the pins 21 and 22); such division of the shearing stresses improves the working conditions for the pins 21 and 22, and enables the pulling power of the winch to be increased.

6. The very great bearing surface of each eccentric 40 or 140 allows providing in the compact bulk thereof a cavity 62 which constitutes a sealed grease tank, the latter being filled with grease only once, at the time of the assembly (FIGS. 5 and 6).

I claim:

1. A gripping apparatus for a free cable winch, comprising. in combination:

a first jaw member;

a second jaw member disposed adjacent said first jaw member to form with said first jaw member a passageway through which a cable may selectively be pulled and clamped;

7 substantially round eccentric push means bearing directly against and mating with said first jaw member:

first strap means embracing one end of said first and second jaw members.

second strap means embracing the other end of said first and second jaw members.

first pivot means disposed on one side of said cable passageway. said first pivot means extending through apertures having completely closed peripheries provided in said strap means, in said second jaw member, and in said eccentric push means to pivotally interconnect said first and second strap means, respectively, and said eccentric push means with said second jaw member;

link means;

second pivot means disposed on the other side of said cable pivotally interconnecting said link means and said first and second strap means; and resilient means connected between said second jaw member and said first strap means urging said jaw members to clamp together against said cable under the action of said eccentric push means, and

wherein each of said strap means has a transverse bottom, the inner surface of which is provided with an aperture adapted to receive one of said eccentric push means.

2. A gripping apparatus characterized substantially in accordance with claim 1, wherein:

said first jaw member comprises an inner jaw;

said second jaw member comprises a U-shaped outer jaw;

said inner jaw is adapted to move within said U- shaped outer jaw by which said inner jaw is surrounded;

said jaws together defining said passageway for receiving said cable;

said first strap means comprises a first strap;

said second strap means comprises a second strap;

said eccentric push means comprises a push eccentric having the shape of an arc of a circle;

each of said straps has a transverse bottom the inner surface of which is provided with one of said push eccentrics which eccentric bears on the back of the inner jaw, while each strap pivots about a transverse pin which is likewise located behind the bottom of said inner jaw at a location which is set over with respect to said push eccentric;

said link means includes at least one pivoted link;

said resilient means comprises a spring; and

the free ends of the arms of one of said straps beyond said outer jaw being connected, on the one hand, to a stop on said outer jaw by said spring tending to rock said strap in the direction in which said jaws are clamped under the action of the set over push eccentrics, and, on the other hand, to the free ends of the arms of the other strap by at least one pivoted link.

3. A gripping apparatus characterized in accordance with claim 2, wherein at least one of said straps is provided with means ensuring the positive driving thereof through swinging about the axis pin thereof.

4. A gripping apparatus substantially in accordance with claim 3, characterized in that the positive driving means includes a small arm provided with a hole and oil welded to the back of the corresponding strap, which arm is intended for receiving the pivot pin for a connecting rod or a control lever.

5. A gripping apparatus substantially in accordance with claim 2, characterized in that each push eccentric is connected to the back of said innerjaw through a bidirectional connection which ensures a desmodromic or positive control of said jaws, both for driving them away from each other and bringing them toward each other.

6. A gripping apparatus characterized substantially in accordance with claim 5, wherein the connection between each push eccentric and the back of said inner jaw is obtained by pivotally mounting said push eccentric in a female housing in the back of said inner jaw, and said housing surrounding the eccentric for more than 180.

7. A gripping apparatus characterized substantially in accordance with claim 6, wherein, after mounting each push eccentric in a hollow defining an angle equal to or less than l80 on the back of said inner jaw, a small block is fixed to the back of said inner jaw, and said block has a bearing in the shape of an arc of a circle which closes behind the push eccentric and cooperates with the hollow to define the female housing.

8. A gripping apparatus substantially in accordance with claim 6, characterized in that the back of said inner jaw is provided with a transverse dove tailed slot between each female housing associated with each push eccentric, and in said slot two tenons come to fit transversely and in back-to-back relation, said tenons being each provided on the base of one of two small blocks, one block for each eccentric.

9. A gripping apparatus according to claim 8, including a screw which passes through half-notches provided in opposite relation on the backs of the small blocks, and which is fixed in a tapped hole in the jaw so that the main operation stresses are not borne by said screw, but by the tenon and slot assembly since the screw head straddles the small blocks.

10. A gripping apparatus characterized substantially in accordance with claim 2, wherein:

each said push eccentric is provided at the top with a projection or boss which is nested into a corresponding opening in the bottom of the strap before the assembly is welded so as to obtain a particularly rigid structure;

at least one of said push eccentrics is provided with a rear heel adapted to abut a bearing face on said inner jaw to limit the rocking amplitude ofthe strap associated therewith in the direction in which said jaws are loosened:

one of the ends of said spring, which ensures selfclamping of the jaws, bears against a finger on a shaft integral with said U-shaped jaw, while the other end of said spring bears against a small plate provided with a central finger and disposed against a shoulder integrally formed with one ofthe straps, this latter spring end ending in a hook fitted to the axis pin through which said strap is linked to the link means: and

a cavity is provided in each push eccentric. said cavity comprising a sealed grease tank.

=l l= l =l 

1. A gripping apparatus for a free cable winch, comprising, in combination: a first jaw member; a second jaw member disposed adjacent said first jaw member to form with said first jaw member a passageway through which a cable may selectively be pulled and clamped; substantially round eccentric push means bearing directly against and mating with said first jaw member; first strap means embracing one end of said first and second jaw members; second strap means embracing the other end of said first and second jaw members; first pivot means disposed on one side of said cable passageway, said first pivot means extending through apertures having completely closed peripheries provided in said strap means, in said second jaw member, and in said eccentric push means to pivotally interconnect said first and second strap means, respectively, and said eccentric push means with said second jaw member; link means; second pivot means disposed on the other side of said cable pivotally interconnecting said link means and said first and second strap means; and resilient means connected between said second jaw member and said first strap means urging said jaw members to clamp together against said cable under the action of said eccentric push means, and wherein each of said strap means has a transverse bottom, the inner surface of which is provided with an aperture adapted to receive one of said eccentric push means.
 1. A gripping apparatus for a free cable winch, comprising, in combination: a first jaw member; a second jaw member disposed adjacent said first jaw member to form with said first jaw member a passageway through which a cable may selectively be pulled and clamped; substantially round eccentric push means bearing directly against and mating with said first jaw member; first strap means embracing one end of said first and second jaw members; second strap means embracing the other end of said first and second jaw members; first pivot means disposed on one side of said cable passageway, said first pivot means extending through apertures having completely closed peripheries provided in said strap means, in said second jaw member, and in said eccentric push means to pivotally interconnect said first and second strap means, respectively, and said eccentric push means with said second jaw member; link means; second pivot means disposed on the other side of said cable pivotally interconnecting said link means and said first and second strap means; and resilient means connected between said second jaw member and said first strap means urging said jaw members to clamp together against said cable under the action of said eccentric push means, and wherein each of said strap means has a transverse bottom, the inner surface of which is provided with an aperture adapted to receive one of said eccentric push means.
 2. A gripping apparatus characterized substantially in accordance with claim 1, wherein: said first jaw member comprises an inner jaw; said second jaw member comprises a U-shaped outer jaw; said inner jaw is adapted to move within said U-shaped outer jaw by which said inner jaw is surrounded; said jaws together defining said passageway for receiving said cable; said first strap means comprises a first strap; said second strap means comprises a second strap; said eccentric push means comprises a push eccentric having the shape of an arc of a circle; each of said straps has a transverse bottom the inner surface of which is provided with one of said push eccentrics which eccentric bears on the back of the inner jaw, while each strap pivots about a transverse pin which is likewise located behind the bottom of said inner jaw at a location which is set over with respect to said push eccentric; said link means includes at least one pivoted link; said resilient means comprises a spring; and the free ends of the arms of one of said straps beyond said outer jaw being connected, on the one hand, to a stop on said outer jaw by said spring tending to rock said strap in the direction in which said jaws are clamped under the action of the set over push eccentrics, and, on the other hand, to the free ends of the arms of the other strap by at least one pivoted link.
 3. A gripping apparatus characterized in accordance with claim 2, wherein at least one of said straps is provided with means ensuring the positive driving thereof through swinging about the axis pin thereof.
 4. A gripping apparatus substantially in accordance with claim 3, characterized in that the positive driving means includes a small arm provided with a hole and welded to the back of the corresponding strap, which arm is intended for receiving the pivot pin for a connecting rod or a control lever.
 5. A gripping apparatus substantially in accordance with claim 2, characterized in that each push eccentric is connected to the back of said inner jaw through a bI-directional connection which ensures a desmodromic or positive control of said jaws, both for driving them away from each other and bringing them toward each other.
 6. A gripping apparatus characterized substantially in accordance with claim 5, wherein the connection between each push eccentric and the back of said inner jaw is obtained by pivotally mounting said push eccentric in a female housing in the back of said inner jaw, and said housing surrounding the eccentric for more than
 180. 7. A gripping apparatus characterized substantially in accordance with claim 6, wherein, after mounting each push eccentric in a hollow defining an angle equal to or less than 180* on the back of said inner jaw, a small block is fixed to the back of said inner jaw, and said block has a bearing in the shape of an arc of a circle which closes behind the push eccentric and cooperates with the hollow to define the female housing.
 8. A gripping apparatus substantially in accordance with claim 6, characterized in that the back of said inner jaw is provided with a transverse dove tailed slot between each female housing associated with each push eccentric, and in said slot two tenons come to fit transversely and in back-to-back relation, said tenons being each provided on the base of one of two small blocks, one block for each eccentric.
 9. A gripping apparatus according to claim 8, including a screw which passes through half-notches provided in opposite relation on the backs of the small blocks, and which is fixed in a tapped hole in the jaw so that the main operation stresses are not borne by said screw, but by the tenon and slot assembly since the screw head straddles the small blocks. 